Combustion heating devices such as oil and gas fired furnaces produce heat by burning oil or gas within a combustion chamber in a heat exchanger and exhausting the products of combustion through an exhaust vent. Room air or other fluid to be heated is circulated around the heat exchanger thereby being heated. With the recent dramatically increased cost of fuels, the efficiency of such devices has become of greatly increased significance. The loss of heat which occurs through venting of the combustion chamber to the outside when the burner is not fired, represents a potential energy saving which could be realized if the vent were closed after discontinuance of the burner operation. The heated gases within the combustion chamber could be retained allowing continued heat extraction from the heat exchanger which would otherwise be lost to the outside. Diverters for mixing room air with the exhaust gases are commonly used and loss of warm room air could also be reduced, as well as backdrafts if the exhaust vent were blocked whenever the heating device was not in operation.
Automatic vent damper devices of this sort have thus long been proposed and utilized. A complicating factor in their design is that of adequate safety features, since if the vent damper were closed during burner operation, overheating could occur and the products of combustion could enter the occupied spaces of the building. Such gases being toxic, their potential leakage presents a considerable health hazard, while the high temperatures could produce a fire.
This safety problem is particularly acute because of the extended time periods during which the furnace operates without maintenance. The life of typical furnaces is sufficiently long that any such automatic vent damper operating devices should operate reliably for a considerable period of years with minimal maintenance.
Any such device should also function properly in the eventuality of to-be-expected malfunctions, i.e., power failures, failure of the burner controls, valve failures in which the burner valve remains in the stuck open position even though the controls are calling for cessation of burner operation.
Additionally, these devices should be able to endure wide variations in temperature and the effects of a humid, rust-inducing environment which over a period of years could result in the sticking or jamming of moving parts such as the damper plates.
The controls for such a device should also ideally be free from regular maintenance requirements.
In some automatic vent damper devices which have heretofore been utilized, the damper is opened by sensing of abnormally high temperatures by a thermostatic device which causes the damper actuator to open the damper. However, when the damper is opened, the vent cools sufficiently such that the thermostatic device damper again is allowed to be closed causing a recycling while the initial failure may go undetected.
Another similar problem is encountered in those systems in which a backup control is built into the system such that upon failure of one control component, another control component acts to take over and produce the proper control of the fuel or damper actuator. Similarly, the failure of the first component will not be detected since the heating device may still be operated. In this event, an undetected failure may continue to be unserviced until a final failure occurs, which the fail-safe design no longer can accommodate.
Another disadvantage of the thermostatic devices typically utilized in these designs is that they cannot be made to respond reliably to a given temperature over the periods of service required. Thus, reliable damper opening temperature may not be achieved over the service life of the actuator.
Another approach has involved the use of a fusible mechanical connection in the damper actuator which provides the driving connection tending to close the damper. The fusible connection melts when a high temperature condition develops indicating burner function to allow a damper open bias actuator such as a weight or spring to open the damper.
This approach is described and claimed in the above-referenced parent application.
While offering the advantage of reliably opening the damper in the event of burner operation, the fusible connection is difficult to design without encountering plastic creep at temperatures below the proper fusing temperature.
It is, accordingly, an object of the present invention to provide an automatic vent damper device for combustion heating devices which is failsafe in operation, in that if the burner operation continues, the damper is moved to the open position regardless of the condition of the system controls.
It is yet another object of the present invention to provide an automatic vent damper operating device in which the failures of the burner controls result in a reliable opening of the vent damper in response to the resultant build-up of high temperature conditions.
It is yet another object of the present invention to provide an automatic vent damper device in which the effects of corrosive conditions or high temperatures are resisted to greatly reduce the incidence of jamming or malfunction of the damper blade.
It is still another object of the present invention to provide such an automatic vent damper device in which upon a failure of the system such as to require the functioning of the failsafe feature, burner operation is interrupted so that the malfunction becomes apparent.
It is yet another object of the present invention to provide a temperature sensitive vent damper which accurately and reliably responds to a predetermined temperature level to cause the damper to be opened.